The need exists to correctly diagnose mechanical degradation of total joint replacements. The efficacy of in-vivo joint monitoring by means of acoustic emission has been demonstrated. To further develop the technique of in-vivo monitoring, the acoustic emission waveform characteristics will be analyzed using correlation plots and together with the attenuation results will be used to optimize the electronic equipment through proper choice of waveform filters. The development of acoustic emission monitoring requires continuation of an ongoing program to monitor patients from the Hip and Knee Clinics of The Hospital for Special Surgery who are clinically considered to be at high risk of mechanical failure. Correlation of acoustic emission results with other clinical findings will provide a basis for clinical interpretation of acoustic emission results. The mechanisms which generate acoustic emission will be further examined. Acoustic emission resulting from failures in implant materials such as bone and polymethylmethacrylate did not correlate well with results from in-vivo monitoring. Therefore, the contribution of interface failure and cancellous bone failure as the most probable sources of acoustic emission will be investigated with in-vitro experiments and finite element analysis. Composite models will be monitored during loading. Specialized finite element analysis capabilities aimed at determining failure loads and locations in interfaces will be used to correlate acoustic emission results (both experimental and clinical) with analytical predictions.